DU NOYER — BITUMINOUS COAL OF THE ARIGNA DISTRICT. 83 



flaggy grits of the basal 

 coal-measures. Above this, 

 and forming the rugged 

 scaur on the brow of the 

 mountain, are the " Bottom 

 Sandstones," or seat-rock 

 of the coals ; above them 

 are the two coal-beds ; the 

 " crops " of which are de- 

 fined by the level surface 

 of the underlying sand- 

 stones, at either side of the 

 mountain. 



The summit is formed of 

 sandstones, with dark grey 

 shales, flaggy grits, and 

 some nodular bands of clay 

 ironstone (see Section). 



The mountain to the 

 extreme right is Altagow- 

 lan,and the two coal "crops" 

 near its summit are clear- 

 ly defined on its northern 

 side, by the low precipitous 

 faces of the sandstones 

 with which the coals are as- 

 sociated. 



By reference to the ac- 

 companying Sections, Nos. 

 1 and 2, the physical struc- 

 ture of both these moun- 

 tains will be at once under- 

 stood. 



In order to afford a still 

 clearer notion of the vast 

 amount of denudation to 

 which the whole of this dis- 

 trict has been subjected, I 

 give the subjoined diagram- 

 matic section across it, from 



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